<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>Chapter 3. The DB Replication Manager</title>
    <link rel="stylesheet" href="gettingStarted.css" type="text/css" />
    <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
    <link rel="start" href="index.html" title="Getting Started with Replicated Berkeley DB Applications" />
    <link rel="up" href="index.html" title="Getting Started with Replicated Berkeley DB Applications" />
    <link rel="prev" href="simpleprogramlisting.html" title="Program Listing" />
    <link rel="next" href="rep_init_code.html" title="Starting and Stopping Replication" />
  </head>
  <body>
    <div xmlns="" class="navheader">
      <div class="libver">
        <p>Library Version 11.2.5.3</p>
      </div>
      <table width="100%" summary="Navigation header">
        <tr>
          <th colspan="3" align="center">Chapter 3. The DB Replication Manager</th>
        </tr>
        <tr>
          <td width="20%" align="left"><a accesskey="p" href="simpleprogramlisting.html">Prev</a> </td>
          <th width="60%" align="center"> </th>
          <td width="20%" align="right"> <a accesskey="n" href="rep_init_code.html">Next</a></td>
        </tr>
      </table>
      <hr />
    </div>
    <div class="chapter" lang="en" xml:lang="en">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title"><a id="repapp"></a>Chapter 3. The DB Replication Manager</h2>
          </div>
        </div>
      </div>
      <div class="toc">
        <p>
          <b>Table of Contents</b>
        </p>
        <dl>
          <dt>
            <span class="sect1">
              <a href="repapp.html#repmgr_grpmgmt">The DB_SITE Handle</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="rep_init_code.html">
        Starting and Stopping Replication
    </a>
            </span>
          </dt>
          <dd>
            <dl>
              <dt>
                <span class="sect2">
                  <a href="rep_init_code.html#election_flags">Managing Election Policies</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="rep_init_code.html#thread_count">Selecting the Number of Threads</a>
                </span>
              </dt>
            </dl>
          </dd>
          <dt>
            <span class="sect1">
              <a href="repmgr_init_example_c.html">Adding the Replication Manager to
                <span>ex_rep_gsg_simple</span>
                
                
        </a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="fwrkpermmessage.html">Permanent Message Handling</a>
            </span>
          </dt>
          <dd>
            <dl>
              <dt>
                <span class="sect2">
                  <a href="fwrkpermmessage.html#fmwrkpermpolicy">Identifying Permanent Message Policies</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="fwrkpermmessage.html#fmwrkpermtimeout">Setting the Permanent Message Timeout</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="fwrkpermmessage.html#perm2fmwrkexample">Adding a Permanent Message Policy to 
                            <span>ex_rep_gsg_repmgr</span>
                            
                            
                    </a>
                </span>
              </dt>
            </dl>
          </dd>
          <dt>
            <span class="sect1">
              <a href="electiontimes.html">Managing Election Times</a>
            </span>
          </dt>
          <dd>
            <dl>
              <dt>
                <span class="sect2">
                  <a href="electiontimes.html#electiontimeout">Managing Election Timeouts</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="electiontimes.html#electretrytime">Managing Election Retry Times</a>
                </span>
              </dt>
            </dl>
          </dd>
          <dt>
            <span class="sect1">
              <a href="fmwrkconnectretry.html">Managing Connection Retries</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="heartbeats.html">Managing Heartbeats</a>
            </span>
          </dt>
        </dl>
      </div>
      <p>
        The easiest way to add replication to your transactional
        application is to use the Replication Manager. The Replication Manager provides a comprehensive
        communications layer that enables replication. For a brief listing
        of the Replication Manager's feature set, see 
        <a class="xref" href="apioverview.html#repframeworkoverview" title="Replication Manager Overview">Replication Manager Overview</a>.
    </p>
      <p>
        To use the Replication Manager, you make use of a combination of the
        <code class="classname">DB_SITE</code>
        
        class and related methods, plus special methods off the
        <span><code class="classname">DB_ENV</code> class.</span>
        
        That is: 
    </p>
      <div class="orderedlist">
        <ol type="1">
          <li>
            <p>
                Create an environment handle as normal.
            </p>
          </li>
          <li>
            <p>
                Configure your environment handle as needed (e.g. set the
                error file and error prefix values, if desired).
            </p>
          </li>
          <li>
            <p>
                Use the Replication Manager replication classes and methods to configure
                the Replication Manager.  Using these classes and methods causes DB
                to know that you are using the Replication Manager.
            </p>
            <p>
                Configuring the Replication Manager entails setting the replication
                environment's priority, setting the TCP/IP address that
                this replication environment will use for incoming
                replication messages, identifying TCP/IP addresses of other
                replication environments, setting the number of replication
                environments in the replication group, and so forth.  These
                actions are discussed throughout the remainder of this
                chapter.
            </p>
          </li>
          <li>
            <p>
                Open your environment handle. When you do this, be sure to
                specify 

                <span>
                    <code class="literal">DB_INIT_REP</code> and
                    <code class="literal">DB_THREAD</code> to your open flags. (This
                    is in addition to the flags that you normally use for a
                    single-threaded transactional application).  The first
                    of these causes replication to be initialized for the
                    application. The second causes your environment handle
                    to be free-threaded (thread safe). Both flags are
                    required for Replication Manager usage.
                </span>
                
                
            </p>
          </li>
          <li>
            <p>
                Start replication by calling
                <span><code class="methodname">DB_ENV-&gt;repmgr_start()</code>.</span>
                
                
            </p>
          </li>
          <li>
            <p>
                Open your databases as needed. Masters must open their databases
                for read and write activity. Replicas can open their databases
                for read-only activity, but doing so means they must
                re-open the databases if the replica ever becomes a master.
                Either way, replicas should never attempt to write to the
                database(s) directly.
            </p>
          </li>
        </ol>
      </div>
      <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
        <h3 class="title">Note</h3>
        <p>
            The Replication Manager allows you to only use one environment handle per
            process.
        </p>
      </div>
      <p>
        When you are ready to shut down your application: 
    </p>
      <div class="orderedlist">
        <ol type="1">
          <li>
            <p>
                Close any open 
                <code class="classname">DB_SITE</code>
                
                handles that you might have open.
            </p>
          </li>
          <li>
            <p>
                Close your databases
            </p>
          </li>
          <li>
            <p>
                Close your environment. This causes replication to stop as
                well.
            </p>
          </li>
        </ol>
      </div>
      <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
        <h3 class="title">Note</h3>
        <p>
            Before you can use the Replication Manager, you may have to enable it
            in your DB library. This is
            <span class="emphasis"><em>not</em></span> a requirement for Microsoft
            Windows systems, or Unix systems that use pthread
            mutexes by default. Other systems, notably BSD and
            BSD-derived systems (such as Mac OS X), must enable the
            Replication Manager when you configure the DB build.
        </p>
        <p>
            You do this by <span class="emphasis"><em>not</em></span> disabling
            replication and by configuring the library with POSIX
            threads support. In other words, replication must be
            turned on in the build (it is by default), and POSIX
            thread support must be enabled if it is not already by
            default.  To do this, use the
            <code class="literal">--enable-pthread_api</code> switch on the
            configure script.
        </p>
        <p>
            For example:
        </p>
        <pre class="programlisting">../dist/configure --enable-pthread-api</pre>
      </div>
      <div class="sect1" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title" style="clear: both"><a id="repmgr_grpmgmt"></a>The DB_SITE Handle</h2>
            </div>
          </div>
        </div>
        <p>
        Before continuing, it is useful to mention the
        <code class="classname">DB_SITE</code>
        
        handle.  This class is used to configure important attributes about
        a site such as its host name and port number, and whether it is the
        local site. It is also used to indicate whether a site is a 
        <span class="emphasis"><em>group creator</em></span>, which is important when you are
        starting the very first site in a replication group for the very
        first time.
    </p>
        <p>
        The
        <code class="classname">DB_SITE</code>
        
        handle is used whenever you start up a site. It must be closed
        before you close your 
        <code class="classname">DB_ENV</code>
        
        handle.
    </p>
        <p>
        The 
        <code class="classname">DB_SITE</code>
        
        handle is plays an important role in replication group management. This topic
        is fully described in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
    </p>
      </div>
    </div>
    <div class="navfooter">
      <hr />
      <table width="100%" summary="Navigation footer">
        <tr>
          <td width="40%" align="left"><a accesskey="p" href="simpleprogramlisting.html">Prev</a> </td>
          <td width="20%" align="center"> </td>
          <td width="40%" align="right"> <a accesskey="n" href="rep_init_code.html">Next</a></td>
        </tr>
        <tr>
          <td width="40%" align="left" valign="top">Program Listing </td>
          <td width="20%" align="center">
            <a accesskey="h" href="index.html">Home</a>
          </td>
          <td width="40%" align="right" valign="top"> 
        Starting and Stopping Replication
    </td>
        </tr>
      </table>
    </div>
  </body>
</html>
